This invention relates generally to use of ultraviolet photocatalytic oxidation (UV-PCO) technology for improved decontamination of fluid in fluid purifier systems, especially in air purifier systems. More specifically, the present invention relates to a device for reducing the deactivation of photocatalytically active oxides used in UV-PCO technology by volatile silicon-containing compounds.
Some buildings utilize air purification systems to remove airborne substances such as benzene, formaldehyde, and other contaminants from the air supply. Some of these purification systems include photocatalytic reactors that utilize a substrate or cartridge containing a photocatalyst oxide. When placed under an appropriate light source; typically a UV light source, the photocatalyst oxide interacts with airborne water molecules to form hydroxyl radicals. The hydroxyl radicals then attack the contaminants and initiate an oxidation reaction that converts the contaminants into less harmful compounds, such as water and carbon dioxide. It is further believed that the combination of water vapor, suitably energetic photons and a photocatalyst also generates an active oxygen agent like hydrogen peroxide (W. Kubo and T. Tatsuma, Analytical Sciences 20 2004 591-593).
A commonly used UV photocatalyst is titanium dioxide (TiO2), otherwise referred to as titania. Degussa P25 titania and tungsten oxide grafted titania catalysts (such as tungsten oxide on P25) have been found to be especially effective at removing organic contaminants under UV light sources.
A problem with air purification systems using UV-PCO technology has arisen. Currently available systems exhibit a significant loss in catalytic ability over time. This loss of catalytic ability has been attributed to volatile silicon-containing compounds (VSCCs), such as certain siloxanes, in the air.
The aggregate amount of volatile organic compounds (VOCs) in air is typically on the order of 1 part per million by volume. In contrast, VSCC concentrations are two or more orders of magnitude lower. These VSCCs arise primarily from the use of certain personal care products, such as deodorants, shampoos, and the like, or dry cleaning fluids. They can also arise from the use of RTV silicone caulks, adhesives and the like. When these VSCCs are oxidized on the photocatalyst of a UV-PCO system, they form relatively non-volatile compounds containing silicon and oxygen that may deactivate the photocatalyst. Examples of non-volatile compounds of silicon and oxygen include silicon dioxide, silicon oxide hydride, silicon hydroxide, high order polysiloxanes and the like. These compounds may be at least partially hydrated when water vapor is present. Increasing the catalyst surface area does not necessarily slow the rate of deactivation as might be expected if the deactivation occurred by direct physical blockage of the active sites by the resultant non-volatile compound containing silicon and oxygen.
There is a need for improved UV-PCO systems that can aid in the elimination of fluid borne contaminants in a fluid purifier and can operate effectively in the presence of typically encountered levels of volatile silicon-containing compounds such as siloxanes.